Lead-free Inorganic Perovskite Cs-Cu-I Embedded Waterproof Nanofiber Films for White Color Emission

doi:10.21203/rs.3.rs-1955168/v1

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Lead-free Inorganic Perovskite Cs-Cu-I Embedded Waterproof Nanofiber Films for White Color Emission

https://doi.org/10.21203/rs.3.rs-1955168/v1

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Organic polymers can enhance the environmental stability of inorganic perovskite nanocrystals (IPNCs) by encapsulation. We fabricated lead-free IPNCs embedded in waterproof and luminous polymer fibers. The encapsulated CsCu₂I₃ and Cs₃Cu₂I₅ nanocrystals within polystyrene (PS) polymers, CsCu₂I₃@PS (Y-fiber) and Cs₃Cu₂I₅@PS (B-fiber) were prepared by one-step electrospinning of the precursor solutions containing the precursors (CsI and CuI) and PS. The embedded nanocrystals had highly uniform sizes, spatial distribution, well-developed crystal structure, and pure phases. The Y-fibers and B-fibers showed bright yellow and blue color emission under ultraviolet (UV) light, respectively, and a white emission fiber layer was fabricated via dual-nozzle co-electrospinning using yellow-emissive CsCu₂I₃, and blue-emissive Cs₃Cu₂I₅ precursor solutions. The as-prepared B-fibers exhibited improved water stability without changing crystal structure and PL emission in deionized water for 20 days. To enhance environmental stability and mechanical properties, the transparent polydimethylsiloxane (PDMS) films containing IPNCs@PS fibers presented strong PL emission without a shift in PL emission wavelength under 100% tensile strain, indicating highly flexible and humidity-durable characteristics.

Lead-free Inorganic Perovskite

Hybrid fiber

Emission-color tuning ᆞElectrospinningᆞwaterproof perovskite

All-inorganic CsPbX₃ perovskites (X = Cl, Br, and I) are considered promising materials for diverse applications such as photovoltaics [1], light emitting diodes (LED) [2], and photodetectors [3], due to their intriguing optoelectronic properties [4, 5]. Although excellent results have been reported in the research and application of lead halides, their commercialization is still limited by the toxicity of Pb and the poor stability of the materials. To address this issue, it is necessary to develop high stability, eco-friendly broadband emission materials. Recently, many types of lead-free perovskites have been studied to replace toxic metallic lead with other non-toxic metals, such as tin halide (CsSnBr₃, Cs₄SnBr₆) [6, 7], bismuth halide (Cs₃Bi₂Br₉) [8], indium halide (Cs₂InBr₅) [9], and copper halide (Cs₃Cu₂I₅, CsCu₂I₃) [10, 11] based perovskites.

Cesium copper halide perovskites (Cs-Cu-X) are representative light emitting materials that are low cost, earth abundant, and provide eco-friendly broadband emission. Synthesis of Cs-Cu-X compounds has been accomplished using solvent evaporation [12], mechanochemical reaction [11, 13], QDs in surfactants [14, 15], melt growth [16], and vapor co-deposition [17, 18], which could be used in optoelectronic applications such as anti-counterfeiting [10, 19], polarization [20], and white light-emitting devices (WLEDs) [21, 22]. Despite the various advantages and applications mentioned above, Cs₃Cu₂I₅ perovskite has low stability in moisture, causing transformation into CsCu₂I₃ and weak PL intensity [10, 23].

To maintain the PL emission of IPNCs, appropriate protective layers are required for the encapsulation of IPNCs to prevent environmental humidity. Polymer matrixes offer thermal, moisture, and oxidation stability to IPNCs materials. Several methods are suggested for improving the stability of perovskite materials through polymer coating with waterproof materials [19] or encapsulation within a polymer matrix [20]. Shi et al. demonstrated the reversible conversion between blue-emissive Cs₃Cu₂I₅ and yellow-emissive CsCu₂I₃ and a polymethyl methacrylate (PMMA) layer, which gives blue-emissive Cs₃Cu₂I₅ long-term stability in the water. Wang et al. fabricated Cs₃Cu₂I₅ encapsulated in poly(vinylidene fluoride) (PVDF) nanofiber films by a one-step electrospinning technique. However, these works require complex steps or provide an irregular microparticle shape of electrospun Cs₃Cu₂I₅. The internal structure, composition control, and emission color mixing of lead-free perovskite hybrid nanofibers have been insufficiently investigated.

Here, we report a facile method for in-situ formation of lead-free IPNCs inside polystyrene (PS) at room temperature without organic surfactants via electrospinning of a PS and CsI/CuI precursor solution. The perovskites within PS provide uniform yellow and blue emission with a wide full width at half maximum (FWHM). We utilized a combination of two yellow and blue emission color fibers to fabricate white-light emission fibers films by co-electrospinning with a dual-nozzle system. Our encapsulation methods confirmed that coating IPNCs with PS can effectively prevent dissolution of CsI in the water and maintain blue and yellow emission in deionized water. Also, we prepared highly stretchable and humidity durable IPNCs@PS@PDMS by applying PDMS onto IPNCs@PS fibers. Our strategies offer a low-cost and facile method for creating stable and excellent photoluminescence (PL) materials while restricting the use of surfactants and toxic chemical additives.

Materials: All chemicals were purchased from Sigma-Aldrich and were used as received without further purification including: cesium iodide (CsI, 99.9%), copper(Ⅰ) iodide (CuI, 99.999%), polystyrene (PS, Mw∼192,000), and N,N-dimethylformamide (DMF, 99.5%). Resin and curing agent for PDMS (Sylgard 184) were purchased from Dow Corning.

Precursor of B-fiber

In a 20 mL glass vial, 0.6 mmol CsI and 0.4 mmol CuI were dispersed in DMF, and the mixture was stirred for 30 min. After complete dissolution of the CsI and CuI salts, a 30 wt% PS/DMF solution (1.0 g) and CsI/CuI solution were mixed and stirred for 1 hour at room temperature (Scheme. 1(a)).

Precursor of Y-fiber: For the synthesis of CsCu₂I₃ crystals, 0.2 mmol CsI and 0.4 mmol CuI were dissolved in a DMF and DMSO (1 : 1) mixed solution, and chloroform was quickly added. A white precipitate formed and was centrifuged at 4,0000 rpm for 5 min [21]. In a 20 mL glass vial, CsCu₂I₃ was dispersed in DMF for 30 min. After complete dissolution of the CsCu₂I₃, 30wt% PS/DMF solution (1.0 g) and CsCu₂I₃ solution were mixed and stirred for 1 hour at room temperature (Scheme. 1(a)).

Single and dual-nozzle electrospinning of IPNC@PS fiber

A PS/perovskite mixture solution from a syringe with a stainless steel nozzle (21 G, ID/OD = 0.50/0.80 mm) was released at 0.1 ml/h using a syringe pump. A voltage supplier was connected to the nozzle and 15 kV was applied. The IPNC@PS fiber was collected on the Al foil-wrapped drum collector (15 cm apart at 25 ^oC). Dual-nozzle electrospinning was performed by two nozzles facing each other with a collector in between. Each collector-nozzle distance and other parameters are the same as the single electrospinning condition. After electrospinning, the IPNC@PS fibers on the substrate were heated at 120 ^oC for 1 hour to remove residual solvent from the PS/perovskite mixed solution (Scheme. 1(b)).

Fabrication of IPNC@PS@PDMS films: A template made of a slide glass was attached to the IPNC@PS fiber collected on Al foil. The premixed PDMS in which resin and curing agent were mixed in a volume ratio of 10:1 was poured into the template. After being cured at 100 ^oC for 10 min, the IPNC@PS@PDMS films peeled off from the template and Al foil. The template size was 40 x 70 mm, and 2 ml of the premixed PDMS was used (Scheme. 1(c)).

Characterization

The morphologies and the sizes of the obtained products were observed by Schottky field emission scanning electron microscopy (SEM, JSM-7100F) and field emission transmission electron microscopy (FE-TEM, Tecnai G2 F20). Elemental analyses were performed using an EDS attached to a TEM. X-ray diffraction (XRD) data were collected to study the crystal structures using a Rigaku Ultima IV diffractometer with CuKα radiation (λ = 1.5405 Å). Inductively coupled plasma mass spectra (ICP-MS) were conducted using a NexION 2000 ICP-MS. PL spectra were collected on a F-7000 spectrofluorometer (Hitachi High-Tech Corp). Ultraviolet-visible (UV-Vis) spectra were recorded on a JASCO V-760 spectrometer.

3.1 In-situ growth of Cs-Cu-I@PS fibers and optical properties.

We fabricated IPNCs@PS fibers via the electrospinning process, as shown in Scheme. 1(a), (b). Briefly, precursor solutions were first prepared by blending PS polymer and perovskite precursors in DMF solvent. Two precursor solutions with different chemical compositions were prepared for the yellow and blue emission fibers corresponding to Y and B fiber, respectively. Subsequently, in the electrospinning process, a liquid jet is directed toward the Al foil used as a collector, and perovskites with uniform spatial distributions were immobilized in PS fibers by rapidly evaporating solvent from fibers. Then, highly uniform PL emission of IPNCs within polymer fibers were observed (vide infra).

We controlled the two types of chemical compositions by mixing CuI and CsI to tune the emission color of the IPNC@PS fibers. Blue color emission was indicated by forming Cs₃Cu₂I₅ from perovskite precursors with a molar ratio of CsI and CuI of 3:2. We applied polycrystalline CsCu₂I₃ for yellow emission because of the low solubility of the precursor with a CsI to CuI molar ratio of 1:2 in DMF. Yellow emission of the Y-fiber (CsCu₂I₃@PS) required mild heat treatment at 90 ^oC, probably due to the slow recrystallization rates of CsCu₂I₃. The prepared Y-fibers showed yellow emission under 245 nm wavelength UV light without damaging the fibers, indicating the stability of the encapsulated CsCu₂I₃ within PS polymers against the thermal treatment (Fig. S1).

The single-nozzle electrospun fibers of the two precursor solutions on Al foil (tailored to dimensions of 2.0×2.0 cm²) produced blue, and yellow emission under 245 nm UV light. The dual-nozzle electrospun successfully provided white-light-emitting fibers (Fig. 1(a)). CsCu₂I₃ and Cs₃Cu₂I₅ IPNC were introduced in the fibers and demonstrated highly uniform PL emission. To estimate the contents of both IPNCs within PS fibers, quantitative analyses of the chemical compositions of the fibers were measured by an ICP-MS method as shown in Table S1. Here, PS fibers contained 5.0 wt% IPNC on average, and the stoichiometric molar ratio of the Cs/Cu was 1.40 and 0.50, consistent with theoretical data based on the formula of Cs₃Cu₂I₅, and CsCu₂I₃. In this method, the B-fibers could be electrospun up to 5 cm×10 cm, corresponding to the area of the collector used for electrospinning (Fig. 1(b)). It should be noted that the electrospun fibers were applied on a large-scale area without defects. To observe the morphology and colloidal uniformity of fiber samples, SEM images were collected as shown in (Fig. 1(c), (d)). B-fiber and Y-fiber prepared by the electrospinning method provided uniform and reproducible fiber without the formation of large beads. The average and distribution of their diameters were 686 ± 122 nm, and 697 ± 132 nm, respectively (Fig. 1(c), (d) inset).

To analyze the optical properties of IPNCs@PS, the luminescence spectrum of the as-prepared samples under different excitation wavelengths ranging from 290 to 320 nm were further explored. As shown in Fig. 2(a), (b), the samples exhibited broad band emission peaking at 445 and 570 nm that are consistent with the peak positions of pristine Cs₃Cu₂I₅ and CsCu₂I₃, respectively [10, 24]. Also, the PL spectra measured at different excitation wavelengths offer the same position of a broad peak, where B-fiber showed a strong blue emission with a broad FWHM (81 nm), and Y-fiber showed yellow emission with a broad FWHM (99 nm) for excitation wavelengths of 290 nm and 320 nm, respectively.

To realize white emission, we prepared a mixture of two sources (B-fibers and Y-fibers) using dual-nozzle electrospinning, which was performed using the same experimental conditions as for single-nozzle electrospinning, with a 1:2 ratio of Cs₃Cu₂I₅ to CsCu₂I₃. Figure 2(c) shows the luminescence spectrum of the as-prepared fiber under different excitation wavelengths ranging from 300 to 320 nm. The broadband spectrum shows that the two phases of Cs₃Cu₂I₅ and CsCu₂I₃ in PS fibers cover the full range of visible light. Compared with CsPbX₃@polymer fibers[25], the present B-fibers and Y-fibers provide excellent coverage of their luminescent spectra because of the wide FWHM. The FWHM of Cs₃Cu₂I₅ and CsCu₂I₃ was approximately 81 nm and 99 nm, respectively.

Because the PL intensities of the B-fiber and Y-fiber depend on the excitation wavelengths, controlling excitation wavelengths is critical for producing white light emission films based on the IPNC@PS fibers combining B-fiber and Y-fiber. At excitation wavelengths of 300 nm, blue emission dominates yellow emission, whose CIE coordinate was ultimately (0.24, 0.22). However, at excitation wavelengths of 320 nm, yellow emission dominates blue emission, whose CIE coordinate was ultimately (0.44, 0.48). The CIE coordinate of as-prepared emission fiber was (0.31, 0.31) under an excitation wavelength of 305 nm, which has a comparable area to the best chromaticity coordinate of white emission indicated of (0.32, 0.32) (Fig. 2(d)) [10, 24, 25]. Besides, the correlated color temperature (CCT), the key parameter for the WLED, was also measured to be 6635 K, which suggests its promising potential application in lighting fields.

3.2 Morphology and structural characterization of IPNCs.

To confirm the nanoscale structure and distribution of perovskite nanocrystals in the polymer fiber, we cut the fiber using the focused ion beam (FIB) technique. A gallium ion beam was used as a source, and cross-sectional images of the fiber were taken using a high-resolution transmission electron microscope (HR-TEM).

As shown in Fig. 3(a), the polymer matrix appears in bright contrast, while the perovskite nanocrystals appear dark due to the elements of perovskite, including the higher atomic number elements such as cesium (Cs), copper (Cu), and iodine (I). The perovskite nanocrystals have irregular shapes and sizes because of rapid crystal formation under the one-step electrospinning process, which is due to solvent evaporation conditions.

Interestingly, the perovskite nanocrystals in a PS matrix have well-developed crystallinity. Figure 3(b) shows clear lattice fringe (with lamellar pattern), and the d spacing is about 50Å, which corresponds to a d value of (120) in the PXRD pattern. The magnified image in Fig. 3(c) shows the atomic structure of the perovskite nanocrystals. The diameter of the bright circles was about 3.5 Å, which is indicated as a Cs⁺ atom (≈ 3.34 Å). For clarity, the inset of (c) depicts an image with a schematic model of C atoms presented along the [120] direction.

In Fig. 3(d), the fast Fourier transform (FFT) pattern shows that reflections at 6.87Å, 5.02Å, and 3.95Å are associated with (111), (120), and (02\(\stackrel{-}{2}\)), respectively. The angles between the (111) and (120) vector, and the (111) and (02\(\stackrel{-}{2}\)) are 38.2° and 83.2°, respectively, in good agreement with the angles of the ideal reciprocal lattice of the orthorhombic unit cell. The reciprocal lattice constants of Cs₃Cu₂I₅ perovskites are a* = 0.0701 Å⁻¹, b* = 0.0989 Å⁻¹, c* = 0.0861 Å⁻¹, α* = 90°, β* = 90°, and γ* = 90° [26].

The cross-sectional TEM image of the Y-fiber sample also shows a microstructure similar to the that of the B-fiber sample. Figure 3(e) presents the CsCu₂I₃ perovskite nanocrystals in the polystyrene fiber, for which the crystallinity is comparable to Cs₃Cu₂I₅ crystals. In Fig. 3(f), the FFT pattern indicated the (110) and (1\(\stackrel{-}{1}\)1) planes, and the angle between them is 78.0°, which matches well with the reciprocal lattice of CsCu₂I₃ perovskites (a* = 0.0952 Å⁻¹, b* = 0.0723 Å⁻¹, c* = 0.164 Å⁻¹, α* = 90°, β* = 90°, γ* = 90°) [27]. Although the Cs₃Cu₂I₅ and CsCu₂I₃ perovskite nanocrystals are rapidly crystallized in the polymer matrix, they have a good crystal quality because of low formation energies and low growth temperature. The crystal phases of Cs₃Cu₂I₅ and CsCu₂I₃ perovskites could be controlled by the copper and cesium stoichiometry of the precursor solution. Additionally, the crystal structures of the B-fiber and Y-fiber detached from the collector were studied using XRD pattern to confirm the formation of perovskites within the PS polymer fibers (Fig. 3(g), (h)). The dominant diffraction peaks of B-fiber are consistent with the standard orthorhombic Cs₃Cu₂I₅ patterns, in which the diffraction peaks at 24.15, 25.76, 26.46, and 30.78° correspond to the (122), (312), (222), and (004) planes [26]. In the Y-fiber, the peaks at 10.70, 21.96, 26.12, and 40.32° correspond to the (110), (130), (221), and (042) planes of the orthorhombic phase (Cmcm) [27]. In both samples, the broad peaks at 2θ = 19.5° result from amorphous organic polymer chains. No other peaks were detected above the detection limit, suggesting a high phase purity of perovskite phase and the absence of CsI and CuI salts in PS fibers.

IPNCs@PS fibers also show excellent water stability. The as-prepared B-fibers and Cs₃Cu₂I₅ powder samples were immersed into the deionized water to monitor water stability, where B-fibers maintained a blue emission for 20 days under a 245 nm UV lamp, further confirming the strong stability in the presence of water. Unprotected Cs₃Cu₂I₅ powders changed to CsCu₂I₃ in only 1 minute and decomposed to CuI in water in 5 minutes (Fig. S2(a)). Generally, CsI is dissolved from Cs₃Cu₂I₅ in the presence of moisture due to the high solubility of CsI in water, which leads to the formation of yellow-emissive CsCu₂I₃ product within several minutes [10, 23]. However, the encapsulated Cs₃Cu₂I₅ within PS fibers can effectively prevent the extraction of CsI and maintain long-term stability by protecting water efficiently.

Recently, Cs₃Cu₂I₅ was encapsulated in PMMA as Cs₃Cu₂I₅@PMMA[19] and silica matrix as Cs₃Cu₂I₅/SiO₂[23] to improve stability, which exhibited emission peaks at approximately 445 nm, like the present sample. Cs₃Cu₂I₅/SiO₂ decomposes very fast under humid conditions into CsCu₂I₃ [23], indicating it is not appropriate in light-emitting device applications. Cs₃Cu₂I₅@PMMA composites fabricated by a complicated multi-step process can tolerate 5 days in water [19]. Compared to these previous reports, the stability of present IPNCs@PS is remarkably improved, suggesting that the encapsulation of the IPNCs in PS polymer matrix during the one-step electrospinning process is effective for enhancing resistance against the decomposition reaction of the IPNC samples. To confirm the crystal structure of IPNCs@PS fibers in water treatments, Fig. S2(b) and S3 provide XRD patterns of IPNCs@PS fibers, which exhibit no obvious change, representing excellent water stability. Fig. S2(b) shows that the diffraction patterns for (122) and (222) planes of the B-fiber were maintained in water treatment even after 20 days. The diffraction patterns for (130) and (221) planes in Y-fiber also remained, as shown in Fig. S3. In both samples, the XRD peaks demonstrate perovskite polycrystalline samples and an aluminum hydroxide thin layer on aluminum metal substrates.

3.3 Transparent and flexible IPNCs@PS@PDMS films.

We fabricated free-standing IPNCs@PS@PDMS films by coating PDMS on IPNCs@PS to improve physical strength, elasticity, and enhanced water stability rather than as-prepared IPNCs@PS fibers [28–30] (Fig. 4). The transmittance of IPNCs@PS nanofibers was quite low due to light scattering of exposed PS fiber. The light scattering can be strongly reduced by changing the PS surface environment of IPNCs@PS nanofibers through infiltration of PDMS because the air in the pores between the nanofibers is replaced by the PDMS [31]. The transmittance is influenced by factors such as reflection index, which depends on the refractive index (RI) of the two materials forming the interface. This phenomenon can be described by the formula below [32].

r = [(n_s - n_f) / (n_s + n_f)]²

Here, r is the reflective coefficient, n_s, and n_f are the RIs of the surrounding medium (air, PDMS) and the fibers, respectively. The RIs of air, PDMS and PS nanofiber are 1.00, 1.55, and 1.51, respectively [32, 33]. Thus, the light reflection at PS nanofiber/PDMS interfaces is much less than that at the PS nanofiber/air interfaces, demonstrating higher transmittance for IPNCs@PS@PDMS films than IPNCs@PS nanofibers. The transmittance of the PDMS substrate was approximately 95%, and even after the addition of the IPNCs@PS nanofiber into PDMS, the transmittance was still high, exceeding 80% in the visible wavelength range (Fig. 4(a)). Although the transmittance of IPNCs@PS@PDMS was high due to a reduction of light scattering, it still showed strong PL emission, indicating that changes in light reflection related to the surrounding medium rarely affect PL emission.

IPNCs@PS@PDMS film exhibited strong PL emission under a 245 nm UV lamp after 100% tensile strain (Fig. 4(b)). To analyze the optical properties of IPNCs@PS@PDMS under uniaxial tensile strain, the luminescence spectrum of the as-prepared films was explored under 300 nm and 320 nm excitation wavelengths, respectively. As shown in Fig. 4(c), (d), the samples exhibit emission peaks at 445 and 570 nm that are consistent with known peak positions of Cs₃Cu₂I₅, and CsCu₂I₃, respectively. The PL intensity decreased by approximately 50% at 100% tensile strain because the IPNC density per unit area decreased during stretching, which can be expressed using the following scaling law [28].

I/I₀ ∝ η/η₀ ∝ A₀/A

Here, I, I₀ is luminescence intensity, η, η₀ is the real number density of phosphors, and A, A₀ is active area in the stretched and unstretched states, respectively.

The area of the IPNCs@PS@PDMS increased approximately two-fold at 100% tensile strain compared to the samples without tensile strain. We expect that (i) the decrease in η as A increases, and (ii) the decrease in I as η per unit area decreases. The values of I/I₀ in the luminescence spectrum at 100% tensile strain measured for the fixed area of IPNCs@PS@PDMS sized 1 cm × 1 cm were 0.54 and 0.45 in Y-fiber-PDMS and B-fiber-PDMS, respectively, which is reasonably consistent with the theoretical data.

Although PDMS composites on electrospun nanofibers have been widely reported in creating flexible transparent matrices[34], the optical properties of the perovskite embedded nanofibers into PDMS have rarely been reported to the best of our knowledge. The present IPNCs@PS@PDMS films can be applied on a large-scale area by a simple two-step method without surfactants, showing strong blue and yellow PL emission without a shift of PL peak under tensile strain while demonstrating highly stretchable and physical strength characteristics. Notably, the IPNCs@PS@PDMS film exhibited strong PL emission even after 100% tensile strain and release were repeated up to 100 times (Fig. S4). The perovskites embedded in two matrices of PS and PDMS are strongly emissive Cs-Cu-I perovskites with good physicochemical properties such as highly flexibility, transparency, and resistance to water. Considering the highly flexible and humidity-resistant characteristics, IPNCs@PS@PDMS films have great potential for use in wearable light-emitting devices.

In this study, we successfully fabricated Cs₃Cu₂I₅ and CsCu₂I₃ encapsulated within PS fibers using electrospinning. These fibers showed highly uniform and strong blue and yellow PL emission with no significant defects with high reproducibility. The high-quality white emission film was obtained via mixing of B-fibers and Y-fibers in a facile manner using a dual-nozzle electrospinning resulting in CIE coordinates of (0.31, 0.31), showing a white region with CCT of 6635 K, which is a promising candidate in applications in lighting fields. The as-fabricated B-fiber and Y-fibers exhibited remarkably improved water stabilities by isolating water efficiently due to the smooth, dense PS polymer matrix serves as a passivation layer. In addition, we applied a PDMS elastomer coating on IPNCs@PS. The fabricated materials are transparent, flexible, and stable in the ambient environment. They exhibit strong PL emission without peak shift at 100% tensile strain. IPNCs@PS@PDMS provides a facile and efficient application for cost-efficient and large-scale production, PL emissions can be readily tuned, suggesting their promising applications in optoelectronic devices.

Funding This research was supported by the Basic Research Lab (2022R1A4A1019296) and by Korea Initiative for fostering University of Research and Innovation Program of the National Research Foundation (NRF) funded by the Korean government (MSIT) (No.2020M3H1A1077095). Funding was also provided by Sejong Science Fellowship Grants from the Ministry of Science and ICT of Korea (2021R1C1C2011591) and the Ministry of Science and ICT (2020M3H4A3106354).

Conflict of interest The authors declare no competing interests

Author contributions statement

Yongju Lee, Ji-Hyun Cha, Heejin Kim, Min Wook Lee, and Duk-Young Jung conceived the idea for detailed experiments. Yongju Lee, Ji-Hyun Cha, and Heejin Kim, contributed equally. Yongju Lee, and Heejin Kim performed the experiment and acquired the data. Ja Yeon Lee performed the PL measurements. Yongju Lee, Ji-Hyun Cha, and Duk-Young Jung wrote the main manuscript text. All authors reviewed the manuscript.

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No competing interests reported.

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Lead-free Inorganic Perovskite Cs-Cu-I Embedded Waterproof Nanofiber Films for White Color Emission

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Abstract

Figures

1 Introduction

2 Experimental Sections

3 Results And Discussion

3.1 In-situ growth of Cs-Cu-I@PS fibers and optical properties.

3.2 Morphology and structural characterization of IPNCs.

3.3 Transparent and flexible IPNCs@PS@PDMS films.

4 Conclusion

Declarations

References

Additional Declarations

Supplementary Files

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